Designing photonic switching systems utilizing equalized drivers

ABSTRACT

Designing a photonics switching system is provided. A photonic switch diode is designed to attain each performance metric in a plurality of performance metrics associated with a photonic switching system based on a weighted value corresponding to each of the plurality of performance metrics. A switch driver circuit is selected from a plurality of switch driver circuits for the photonic switching system. It is determined whether each performance metric associated with the photonic switching system meets or exceeds a threshold value corresponding to each of the plurality of performance metrics based on the photonic switch diode designed and the switch driver circuit selected. In response to determining that each performance metric associated with the photonic switching system meets or exceeds the threshold value corresponding to each of the performance metrics, the photonic switching system is designed using the photonic switch diode designed and the switch driver circuit selected.

This invention was made with Government support under Contract No.:W911NF-11-2-0059 (awarded by Defense Advanced Research Projects Agency(DARPA)). The Government has certain rights in this invention.

BACKGROUND

1. Field

The disclosure relates generally to an improved silicon photonic chipand more specifically to designing a photonic switching system thatutilizes an equalized driver to increase performance of photonic switchdiodes located on the silicon photonic chip.

2. Description of the Related Art

Silicon (Si) photonics is a technology that is under worldwide researchand development due to its promise of delivering high performanceoptical components built in low-cost silicon chip technologies. Siliconphotonics is the study and application of photonic systems that usesilicon as an optical medium. The silicon is patterned withsub-micrometer precision into silicon photonic components. The silicontypically lies on top of a layer of silica in what is known assilicon-on-insulator (SOI).

Photonic switches have been considered as a replacement to electricalswitches due to their very large per-port bandwidth enabled bywavelength-division multiplexing, and due to the energy savings providedby the mitigation of optical detection and re-transmission before andafter the electrical switch. Photonic switches, which often leveragephase alteration within forward or reverse biased diodes to achieve pathselectivity, have demonstrated broad spectral operation with lowcrosstalk. Designing a photonic switch can be a complex task, requiringtradeoffs of various performance metrics for an optimized design.Notably, speed of the photonic switch is often traded for or againstother performance metrics in the design of the photonic switch.

SUMMARY

According to one embodiment of the present invention, a method fordesigning a photonic switching system is provided. A data processingsystem designs a photonic switch diode to attain each performance metricin a plurality of performance metrics associated with a photonicswitching system based on a weighted value corresponding to each of theplurality of performance metrics. In addition, the data processingsystem selects an electronic switch driver circuit design from aplurality of electronic switch driver circuit designs for the photonicswitching system. The data processing system determines whether eachperformance metric in the plurality of performance metrics associatedwith the photonic switching system meets or exceeds a threshold valuecorresponding to each of the plurality of performance metrics based onthe photonic switch diode designed by the data processing system and theelectronic switch driver circuit design selected by the data processingsystem. Then, in response to the data processing system determining thateach performance metric in the plurality of performance metricsassociated with the photonic switching system meets or exceeds thethreshold value corresponding to each of the performance metrics, thedata processing system designs the photonic switching system using thephotonic switch diode designed by the data processing system and theelectronic switch driver circuit design selected by the data processingsystem that met or exceeded each threshold value corresponding to eachof the plurality of performance metrics associated with the photonicswitching system based on the weighted value of each performance metric.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a cross-section view of a silicon photonic chipin accordance with an illustrative embodiment;

FIG. 2 is a diagram of a photonic switching system in accordance with anillustrative embodiment;

FIG. 3 is a pictorial illustration of a photonic switching system thatincludes a current mode logic-based driver circuit and a photonic switchdiode in accordance with an illustrative embodiment;

FIG. 4 is a pictorial illustration of an inverter logic-based drivercircuit and a drive waveform that exits the driver circuit in accordancewith an illustrative embodiment;

FIG. 5 is a pictorial illustration of two different photonic switchingsystems in accordance with an illustrative embodiment;

FIG. 6 is a pictorial illustration of a photonic switching system thatincludes two electronic switch driver circuits in accordance with anillustrative embodiment;

FIG. 7 is a flowchart illustrating a process for designing a photonicswitching system in accordance with an illustrative embodiment;

FIG. 8 is a flowchart illustrating a process of an electronic switchdriver circuit in accordance with an illustrative embodiment; and

FIG. 9 is a diagram of a data processing system in accordance with anillustrative embodiment.

DETAILED DESCRIPTION

With reference now to the figures, and in particular, with reference toFIGS. 1-6, diagrams of apparatuses are provided in which illustrativeembodiments may be implemented. It should be appreciated that FIGS. 1-6are only meant as examples and are not intended to assert or imply anylimitation with regard to the apparatuses in which different embodimentsmay be implemented. Many modifications to the depicted apparatuses maybe made.

FIG. 1 depicts a cross-section view of a silicon photonic chip inaccordance with an illustrative embodiment. Silicon photonic chip 100 isan example of a semiconductor chip that may be used in a data processingsystem, such as a computer. In addition, silicon photonic chip 100 iscapable of routing optical signals (i.e., pulses of light), which areused to communicate data. In other words, silicon photonic chip 100 isan optical switching device or an array of such devices. Siliconphotonic chip 100 includes active silicon photonic layer 102, buriedoxide layer 104, and silicon substrate 106.

Active silicon photonic layer 102 is located on a front side of siliconphotonic chip 100. Active silicon photonic layer 102 transports theoptical signals or pulses of light and is typically 150-300 nanometersin thickness. Active silicon photonic layer 102 includes siliconphotonic devices 108, which are essentially transparent to the opticalsignals at a wavelength of approximately 1.1 to beyond 2.0 micrometers.In addition, active silicon photonic layer 102 also includes electronicdevices 110. However, it should be noted that active silicon photoniclayer 102 may include both silicon photonic devices 108 and electronicdevices 110 or may only include silicon photonic devices 108.

The photonic devices (i.e., silicon optical structures) are fabricatedwithin active silicon photonic layer 102. A photonic device is anyoptical structure fabricated in active silicon photonic layer 102 thatguides, generates, manipulates, or detects the pulses of light. Examplesof photonic devices are lasers, optical modulators, photodetectors, andoptical switch diodes, along with silicon optical waveguides 112, whichare used to transport the optical signals to and from the photonicdevices. Examples of electronic devices that may be included in activesilicon photonic layer 102 are transistors, capacitors, resistors, andinductors. A standard process for fabricating these photonic andelectronic devices is a complementary metal oxide-semiconductor (CMOS)process.

Buried oxide layer 104 of silicon photonic chip 100 is buried betweenactive silicon photonic layer 102 and silicon substrate 106. Buriedoxide layer 104 may, for example, be comprised of silicon dioxide (SiO₂)material. Typically, buried oxide layer 104 is greater than or equal toone to two micrometers in thickness.

Silicon substrate 106 is on a backside of silicon photonic chip 100.Silicon substrate 106 is a bulk silicon layer that provides support forsilicon photonic chip 100. Typically, silicon substrate 106 is greaterthan or equal to 300 micrometers.

In the course of developing illustrative embodiments, it was discoveredthat through a process of passivating the sidewalls of the siliconoptical waveguides with a thin layer of silicon nitride (Si₃N₄) thelifetime of an electronic carrier within a photonic switch diode thatenables photonic switching within optical waveguides formed in theactive silicon photonic layer may be altered by two orders of magnitude.This thin layer of silicon nitride has a negligible effect on theoptical mode within the silicon optical waveguide, but has a substantialeffect on surface recombination, thereby influencing the electroniccarrier lifetime for a photonic switch diode constructed across thesilicon optical waveguide. Photonic switch diodes with an increasedcarrier lifetime demonstrate extremely low steady-state powerconsumption, but suffer from decreased reconfiguration speeds.Conversely, photonic switch diodes with a decreased carrier lifetimeenable increased reconfiguration speeds, but require increased amountsof power to hold the photonic switch diode in an ON-state due to theincreased recombination current in the photonic switch diode duringsteady-state operation. Therefore, within photonic switch diodes atrade-off exists between reconfiguration speed and power consumption.

In addition, photonic switch diodes may suffer from decreasedreconfiguration speeds for other reasons. For example, when usingsilicon optical waveguides that have a cross sectional dimension greaterthan one micrometer (μm), the reconfiguration speed of the photonicswitch diode is decreased. Typically, the cross sectional dimension of asilicon optical waveguide is less than 1 micrometer. This increased modesize of the silicon optical waveguide provides increased alignmenttolerances, more efficient optical coupling between the silicon photonicdevices and a standard single-mode optical fiber, and decreased lightpropagation and device insertion losses. However, the increased crosssectional dimension of the silicon optical waveguide requires anincreased length of the photonic switch diode, which leads to decreasedreconfiguration speed of the photonic switch diode or slower operationof the photonic switch diode.

Another example of influencing the reconfiguration speed of the photonicswitch diode is choosing between reverse-biased diodes andforward-biased diodes. Forward-biased diodes have a decreased footprintor size, but also have a significantly slower reconfiguration speed ascompared to reverse-biased diodes. Therefore, photonic switch diodedesigners often sacrifice the low drive voltage associated with theslower reconfiguration speed and smaller footprint achievable with aforward-biased diode design for the reconfiguration speed afforded by areverse-biased diode design.

Thus in each of the examples above, a tradeoff exists between speed ofthe photonic switch diode and other performance metrics, such as powerconsumption of the photonic switch diode, size or footprint of thephotonic switch diode, alignment tolerance of the photonic switch diodewith an optical cable, and cost of the photonic switch diode. However,illustrative embodiments use a system-wide optimization approach thatdesigns the photonic switch diodes in conjunction with selecting acustom electronic switch driver circuit design from a plurality ofelectronic switch driver circuit designs that increases performance ofthe designed photonic switch diodes (e.g., increases the speed of thephotonic switch diodes). The plurality of electronic switch drivercircuit designs may be, for example, a current mode logic design, aninverter logic design, and an inverter logic design coupled with aninductively peaked inverter logic design. Each of these electronicswitch driver circuit designs may employ, for example, feed-forwardequalization techniques and be implemented in a complementary metaloxide-semiconductor driver.

Illustrative embodiments by using this system-wide optimization approachincrease the speed of the photonic switch diode by customizing theswitch drivers. Consequently, the design of the photonic switch diodecan sacrifice speed performance of the photonic switch diode for gainsin optical coupling efficiency, footprint, power consumption, and costwith no loss in the speed of the overall photonic switching system,which includes the photonic switch diode and the electronic switchdriver circuit. As a result, illustrative embodiments break the inherentspeed tradeoffs in photonic switch design by selecting the appropriateswitch driver architecture or design that yields an increasedsystem-wide response.

In addition, even though a photonic modulator and a photonic switchdiode may in some cases share similar structures and topologies, theprioritized performance metrics of a photonic modulator and a photonicswitch diode rarely overlap. For example, pre-emphasizing a photonicmodulator is primarily done to increase the bandwidth of the photonicmodulator and is done at the expense of other performance metrics, suchas power consumption. Whereas for a photonic switch diode, illustrativeembodiments leverage pre-emphasis as a means of maintaining thereconfiguration speed of the photonic switch diode while making gains inother critical photonic switching system performance metrics, such aspower consumption, footprint, alignment tolerance, and cost. Thus, itshould be noted that illustrative embodiments are not just simply makingthe photonic switch diode as fast as possible. This distinction isimportant because it leads to different options for the switch drivercircuit design. For example, illustrative embodiments may use acomplementary metal oxide-semiconductor driver based on inverter logicor may use a complementary metal oxide-semiconductor driver based oninverter logic and inductively peaked inverter logic to drive thephotonic switch diode. Alternatively, illustrative embodiments may use acomplementary metal oxide-semiconductor driver based on current-modelogic to drive the photonic switch diode. Each of these driver designsmay employ feed-forward equalization.

With reference now to FIG. 2, a diagram of a photonic switching systemis depicted in accordance with an illustrative embodiment. Photonicswitching system 200 is a system of components designed to increase thespeed of optical signal transmission without increasing other systemperformance metrics, such as power consumption, size, and cost. Photonicswitching system 200 includes electronic switch driver circuit 202 andphotonic switch diode 204.

Electronic switch driver circuit 202 is, for example, a complementarymetal oxide-semiconductor driver that drives photonic switch diode 204by outputting a drive waveform from electronic switch driver circuit 202to photonic switch diode 204 based on an electrical input signalreceived by electronic switch driver circuit 202 from optical packetscheduler 206. Optical packet scheduler 206 schedules optical packetsfor transmission by photonic switch diode 204. Electronic switch drivercircuit 202 generates the drive waveform from the electrical inputsignal received from optical packet scheduler 206 by using one ofinverter logic, inverter logic and inductively peaked inverter logic incombination, or current mode logic.

Photonic switch diode 204 is a photonic device located in an activesilicon photonic layer of a silicon photonic chip, such as one ofsilicon photonic devices 108 located in active silicon photonic layer102 of silicon photonic chip 100 in FIG. 1. In this example, photonicswitch diode 204 is a routing switch for routing optical signals orpackets to an appropriate output port in a plurality of output ports.Also, in this illustrated example, photonic switch diode is shown toinclude one input port and two output ports. However, it should be notedthat photonic switch diode 204 may include any number of input ports andany number of output ports and that the number of input ports and thenumber of outputs does not have to be the same, but may be the same.Further, electronic switch driver circuit 202 and photonic switch diode204 are located on separate chips. However, in an alternativeembodiment, electronic switch driver circuit 202 and photonic switchdiode 204 may be located on the same silicon photonic chip, such aselectronic devices 110 and silicon photonic devices 108 located onsilicon photonic chip 100 in FIG. 1.

With reference now to FIG. 3, a pictorial illustration of a photonicswitching system that includes a current mode logic-based driver circuitand a photonic switch diode is depicted in accordance with anillustrative embodiment. Photonic switching system 300 may be, forexample, photonic switching system 200 in FIG. 2. Photonic switchingsystem 300 includes electronic switch driver circuit 302 and photonicswitch diode 304, such as electronic switch driver circuit 202 andphotonic switch diode 204 in FIG. 2.

In this illustrated example, electronic switch driver circuit 302 is acomplementary metal oxide-semiconductor driver based on current modelogic that employs feed-forward equalization to drive photonic switchdiode 304. Electronic switch driver circuit 302 pre-amplifies anelectrical signal received from an optical packet scheduler, such asoptical packet scheduler 206 in FIG. 2, and applies equalization to theelectronic signal to generate pre-emphasized drive waveform 306, whichis used to drive photonic switch diode 304. It should be noted that inthis illustrated example, solid lines in the circuit schematic denoteelectrical connections, whereas the dashed lines denote optical orphotonic connections.

Photonic switch diode 304, by itself, has a slower step response asshown by photonic switch step response 308, which leads to decreasedreconfiguration speeds of photonic switch diode 304 causing increasednetwork inefficiencies. However, the response of photonic switchingsystem 300, which is photonic switch diode 304 being driven by thecurrent mode logic-based feed-forward equalization driver (i.e.,electronic switch driver circuit 302), shows faster transitions betweenstates of photonic switch diode 304 in photonic switch diode response tothe pre-emphasized drive waveform 310. Further, although photonic switchdiode 304 is illustrated with one input port and two output ports,illustrative embodiments may utilize any integral combination of inputports and output ports in photonic switch diode 304.

Furthermore, it should be noted that even though this illustratedexample demonstrates the efficacy of this approach, current mode logiccircuit designs are not the preferred illustrative embodiment forimplementing the electronic switch driver circuits. Because photonicswitch diode 304 may frequently be held in a steady-state for longperiods of time, the always-on current mode logic tail currents resultin increased average power consumption as compared to inverterlogic-based electronic complementary metal oxide-semiconductor designs.The smaller footprint of the inverter logic-based designs complement thedensity afforded with photonic switch diodes. In addition, inverterlogic-based designs are capable of providing ultra-low steady-statesupply currents, which are beneficial to photonic switching systems thatmay be held in the ON-state or the OFF-state for long periods of time.Co-designing switch drivers using inverter logic in electroniccomplementary metal oxide-semiconductor designs requires a system view,which considers each of the prioritized performance metrics of thephotonic switching system that is often headed up by low steady-statepower dissipation. Unfortunately, a simple approach to an inverter-basedfeed-forward equalization driver that mimics the current mode logiccircuit techniques results in larger supply currents in the steady-stateas shown in the illustration of FIG. 4.

With reference now to FIG. 4, a pictorial illustration of an inverterlogic-based driver circuit and a drive waveform that exits the drivercircuit is depicted in accordance with an illustrative embodiment.Electronic switch driver circuit 400 may be, for example, electronicswitch driver circuit 202 in FIG. 2. In this illustrated example,electronic switch driver circuit 400 is a complementary metaloxide-semiconductor driver based on inverter logic that employsfeed-forward equalization to drive a photonic switch diode, such asphotonic switch diode 204 in FIG. 2. Electronic switch driver circuit400 pre-amplifies an electrical signal received from an optical packetscheduler, such as optical packet scheduler 206 in FIG. 2, and appliesequalization to the electronic signal to generate pre-emphasized drivewaveform 402, which is used to drive the photonic switch diode. As shownin this illustrated example, electronic switch driver circuit 400provides lower currents when the output voltage is held at the supplyrails, but provides higher currents when the output voltage is off ofthe supply rails. A challenge using this approach of a complementarymetal oxide-semiconductor driver design based on inverter logic thatemploys feed-forward equalization is the condition that the circuit'soutput voltage must remain on one of the supply rails as much aspossible in order to maintain lower supply currents and thus lower powerconsumption.

With reference now to FIG. 5, a pictorial illustration of two differentphotonic switching systems is depicted in accordance with anillustrative embodiment. Photonic switching system 502 and photonicswitching system 504 represent preferred illustrative embodiments.Photonic switching system 502 and photonic switching system 504 may be,for example, photonic switching system 200 in FIG. 2.

Photonic switching system 502 includes electronic switch driver circuit506 and photonic switch diode 508, such as electronic switch drivercircuit 202 and photonic switch diode 204 in FIG. 2. In this illustratedexample, electronic switch driver circuit 506 is a complementary metaloxide-semiconductor driver based on inverter logic and inductivelypeaked inverter logic that employs feed-forward equalization to drivephotonic switch diode 508. Electronic switch driver circuit 506pre-amplifies an electrical signal received from an optical packetscheduler, such as optical packet scheduler 206 in FIG. 2, and appliesequalization to the electronic signal to generate pre-emphasized drivewaveform 514, which is used to drive photonic switch diode 508.

Electronic switch driver circuit 506, which is a complementary metaloxide-semiconductor driver design based on inverter logic andinductively peaked inverter logic, leverages inductive peaking inelectronic switch driver circuit 506 to enable overshoot, undershoot, orboth on drive waveform 514 exiting electronic switch driver circuit 506.Pre-emphasized drive waveform 514, which resembles pre-emphasized drivewaveform 306 in FIG. 3, is able to increase the speed performance ofphotonic switching system 502. In particular, the ability to addovershoot to the rising edge of the drive waveform, undershoot to thefalling edge of the drive waveform, or both, enables the selectivespeed-up of only the OFF-state to ON-state transition of the photonicswitch diode, the selective speed-up of only the ON-state to OFF-statetransition of the photonic switch diode, or both, respectively. This isa specific instance of the more general description in paragraph [0040].It should be noted that in the steady-state, pre-emphasized drivewaveform 514 returns to the supply rails where power consumption isminimal.

Photonic switching system 504 includes electronic switch driver circuit510 and photonic switch diode 512, such as electronic switch drivercircuit 202 and photonic switch diode 204 in FIG. 2. In this illustratedexample, electronic switch driver circuit 510 is a complementary metaloxide-semiconductor driver based on inverter logic with inductiveloading that enables overshoot, undershoot, or both on the waveform usedto drive photonic switch diode 512. Electronic switch driver circuit 510pre-amplifies an electrical signal received from the optical packetscheduler and applies equalization to the electronic signal to generatepre-emphasized drive waveform 514, which is used to drive photonicswitch diode 512.

With reference now to FIG. 6, a pictorial illustration of a photonicswitching system that includes two electronic switch driver circuits isdepicted in accordance with an illustrative embodiment. Photonicswitching system 600 illustrates a general implementation and photonicswitching system 614 illustrates a specific implementation of adual-power supply photonic switching system that switches between theoutputs of two electronic switch driver circuits in order to generate adrive waveform of a feed-forward equalization circuit, such aspre-emphasized drive waveform 616. Photonic switching system 600 andphotonic switching system 614 both include two copies of an electroniccomplementary metal oxide-semiconductor driver based on inverter logicwith each driver circuit powered by separate and distinct supplyvoltages.

Photonic switching system 600 includes electronic switch driver circuit602, electronic switch driver circuit 604, electronic switch 606,electronic switch 608, edge detector circuit 610, and photonic switchdiode 612, which is driven from produced pre-emphasized drive waveform616. Photonic switching system 600 uses edge detector circuit 610 andtwo electronic switches 606 and 608 to switch between drive waveformoutputs of electronic switch driver circuit 602 and electronic switchdriver circuit 604 at different times. For example, edge detectorcircuit 610 may output a short electrical pulse that switches the outputvoltage from a driver circuit using a smaller supply voltage to a drivercircuit using a larger supply voltage at each state change of photonicswitch diode 612. The state of photonic switch diode 612 may be changed,for example, between transmission of each optical packet encoded withdata.

In some cases the photonic switch diode may exhibit a slowerreconfiguration speed on only one of the two state changes (i.e., risingedge or falling edge), while the other state change may exhibit a fasterreconfiguration speed. In such a case, the driver circuit can beoptimized through co-design with the photonic switch diode to advancethe speed of the photonic switching system in only one direction (i.e.,on the rising edge or the falling edge). This type of unidirectionaloptimization may be beneficial in decreasing cost, power consumption,and footprint.

With reference now to FIG. 7, a flowchart illustrating a process fordesigning a photonic switching system is shown in accordance with anillustrative embodiment. The process shown in FIG. 7 may be implementedin a data processing system, such as data processing system 900 in FIG.9.

The process begins when the data processing system receives a weightedvalue for each performance metric in a plurality of performance metricsassociated with a photonic switching system that includes a photonicswitch diode and an electronic switch driver circuit (step 702). Thephotonic switching system may be, for example, photonic switching system200 in FIG. 2 that includes electronic switch driver circuit 202 andphotonic switch diode 204. The weighted values for each of the pluralityof performance metrics may be received by the data processing system viauser inputs or may be received from a software application executing onthe data processing system. The plurality of performance metricsassociated with the photonic switching system may be, for example, speedof the photonic switching system, size or footprint of the photonicswitching system, power consumption of the switching system, alignmenttolerance of the photonic switching system with an optical cable, andcost of the photonic switching system. A weighted value is a valueassigned to each of the plurality of performance metrics that indicatesa level of importance of each of the plurality of performance metrics indesigning the photonic switching system. It should be noted thatillustrative embodiments use speed of the photonic switching system asthe primary performance metric in the plurality of performance metrics.Also, it should be noted that illustrative embodiments may utilize moreperformance metrics other than what is listed above.

After receiving a weighted value for each performance metric in step702, the data processing system designs the photonic switch diode toattain each performance metric in the plurality of performance metricsbased on the weighted value received for each of the plurality ofperformance metrics (step 704). In addition, the data processing systemselects an electronic switch driver circuit design from a plurality ofelectronic switch driver circuit designs (step 706). The plurality ofelectronic switch driver circuit designs that the data processing systemselects from may be, for example, a complementary metaloxide-semiconductor driver design based on inverter logic, acomplementary metal oxide-semiconductor driver design based on inverterlogic coupled with inductively peaked inverter logic, and acomplementary metal oxide-semiconductor driver design based on currentmode logic.

Subsequently, the data processing system makes a determination as towhether each performance metric in the plurality of performance metricsassociated with the photonic switching system meets or exceeds athreshold value corresponding to each of the plurality of performancemetrics based on the photonic switch diode designed by the dataprocessing system in step 704 and the electronic switch driver circuitdesign selected by the data processing system in step 706 (step 708).The data processing system may determine that each performance metric inthe plurality of performance metrics meets or exceeds the thresholdvalue corresponding to each of the performance metrics by using, forexample, a simulation program. Alternatively, the data processing systemmay determine that each performance metric in the plurality ofperformance metrics meets or exceeds the threshold value correspondingto each of the performance metrics by analyzing, for example, test data.

If the data processing system determines that each performance metric inthe plurality of performance metrics associated with the photonicswitching system does meet or exceed the threshold value correspondingto each of the plurality of performance metrics based on the photonicswitch diode designed by the data processing system and the electronicswitch driver circuit design selected by the data processing system, yesoutput of step 708, then the data processing system designs the photonicswitching system using the photonic switch diode designed by the dataprocessing system and the electronic switch driver circuit designselected by the data processing system that met or exceeded eachthreshold value corresponding to each of the plurality of performancemetrics associated with the photonic switching system based on theweighted value of each performance metric (step 710). After designingthe photonic switching system in step 710, the data processing systemstores the design of the photonic switching system in a storage device(step 712). The process terminates thereafter.

Returning again to step 708, if the data processing system determinesthat each performance metric in the plurality of performance metricsassociated with the photonic switching system does not meet or exceedthe threshold value corresponding to each of the plurality ofperformance metrics based on the photonic switch diode designed by thedata processing system and the electronic switch driver circuit designselected by the data processing system, no output of step 708, then thedata processing system re-designs the photonic switch diode byincreasing the weighted value of each performance metric that did notmeet or exceed its respective threshold value and decreasing theweighted value corresponding to a speed of the photonic switching system(step 714). Thereafter, the process returns to step 706.

With reference now to FIG. 8, a flowchart illustrating a process of anelectronic switch driver circuit is shown in accordance with anillustrative embodiment. The process shown in FIG. 8 may be implementedin an electronic switch driver circuit, such as, for example, electronicswitch driver circuit 202 in FIG. 2, electronic switch driver circuit302 in FIG. 3, electronic switch driver circuit 506 or electronic switchdriver circuit 510 in FIG. 5, or electronic switch driver circuit 602and electronic switch driver circuit 604 in FIG. 6.

The process begins when the electronic switch driver circuit receives anelectronic control signal input from an optical packet scheduler, suchas optical packet scheduler 206 in FIG. 2, to send an optical signalencoded with data via a photonic switch diode located in a siliconphotonic chip (step 802). The photonic switch diode may be, for example,photonic switch diode 204 in FIG. 2 or photonic switch diode 304 in FIG.3. The silicon photonic chip may be, for example, silicon photonic chip100 in FIG. 1.

After receiving the electronic control signal input from the opticalpacket scheduler to send an optical signal encoded with data via thephotonic switch diode in step 802, the electronic switch driver circuitamplifies the electronic control signal input received from the opticalpacket scheduler and applies equalization to the electronic controlsignal input if necessary to generate a pre-emphasized drive waveform todrive the photonic switch diode (step 804). The pre-emphasized drivewaveform may be, for example, pre-emphasized drive waveform 402 in FIG.4, pre-emphasized drive waveform 514 in FIG. 5, or pre-emphasized drivewaveform 614 in FIG. 6.

In addition, the electronic switch driver circuit waits a predeterminedamount of guard time to ensure that a state of the photonic switch diodehas changed (step 806). In other words, optical signals are not passedthrough the photonic switch diode until state transition has stabilized.An example of a predetermined amount of guard time would be typicallyone nanosecond to tens of nanoseconds. Subsequent to waiting thepredetermined amount of guard time to ensure that the state of thephotonic switch diode has changed in step 806, the electronic switchdriver circuit applies the pre-emphasized drive waveform to the photonicswitch diode to drive the photonic switch diode to transmit the opticalsignal encoded with data from an appropriate output port in a pluralityof output ports located on the photonic switch diode (step 808). Theprocess terminates thereafter.

With reference now to FIG. 9, a diagram of a data processing system isdepicted in accordance with an illustrative embodiment. Data processingsystem 900 is an example of a computer in which computer readableprogram code or instructions implementing processes of illustrativeembodiments may be located. Data processing system 900 may be used toimplement the processes shown in the flowchart of FIG. 7. In otherwords, data processing system 900 may be used to generate a design of aphotonic switching system that utilizes an electronic switch drivercircuit, which amplifies electronic input signals from an optical packetscheduler and applies equalization when necessary, to increaseperformance of photonic switch diodes located in an active siliconphotonic layer of a silicon photonic chip.

In this illustrative example, data processing system 900 includescommunications fabric 902, which provides communications betweenprocessor unit 904, memory 906, persistent storage 908, communicationsunit 910, input/output (I/O) unit 912, and display 914. In this example,communications fabric 902 may take the form of a bus system.

Processor unit 904 serves to execute instructions for software that maybe loaded into memory 906. Processor unit 904 may be a number ofprocessors, a multi-processor core, or some other type of processor,depending on the particular implementation.

Memory 906 and persistent storage 908 are examples of storage devices916. A storage device is any piece of hardware that is capable ofstoring information, such as, for example, without limitation, data,program code in functional form, and/or other suitable informationeither on a temporary basis and/or a persistent basis. Storage devices916 may also be referred to as computer readable storage devices inthese illustrative examples. Memory 906 in these examples may be, forexample, a random access memory or any other suitable volatile ornon-volatile storage device. Persistent storage 908 may take variousforms, depending on the particular implementation.

For example, persistent storage 908 may contain one or more componentsor devices. For example, persistent storage 908 may be a hard drive, aflash memory, a rewritable optical disk, a rewritable magnetic tape, orsome combination of the above. The media used by persistent storage 908also may be removable. For example, a removable hard drive may be usedfor persistent storage 908.

Communications unit 910, in these illustrative examples, provides forcommunications with other data processing systems or devices. In theseillustrative examples, communications unit 910 is a network interfacecard.

Input/output unit 912 allows for input and output of data with otherdevices that may be connected to data processing system 900. Forexample, input/output unit 912 may provide a connection for user inputthrough a keyboard, a mouse, and/or some other suitable input device.Further, input/output unit 912 may send output to a printer. Display 914provides a mechanism to display information to a user.

Instructions for the operating system, applications, and/or programs maybe located in storage devices 916, which are in communication withprocessor unit 904 through communications fabric 902. The processes ofthe different embodiments may be performed by processor unit 904 usingcomputer-implemented instructions, which may be located in a memory,such as memory 906.

These instructions are referred to as program code, computer usableprogram code, or computer readable program code that may be read andexecuted by a processor in processor unit 904. The program code in thedifferent embodiments may be embodied on different physical or computerreadable storage media, such as memory 906 or persistent storage 908.

Program code 918 is located in a functional form on computer readablemedia 920 that is selectively removable and may be loaded onto ortransferred to data processing system 900 for execution by processorunit 904. Program code 918 and computer readable media 920 form computerprogram product 922 in these illustrative examples. In one example,computer readable media 920 may be computer readable storage media 924or computer readable signal media 926. In these illustrative examples,computer readable storage media 924 is a physical or tangible storagedevice used to store program code 918 rather than a medium thatpropagates or transmits program code 918.

Alternatively, program code 918 may be transferred to data processingsystem 900 using computer readable signal media 926. Computer readablesignal media 926 may be, for example, a propagated data signalcontaining program code 918. For example, computer readable signal media926 may be an electromagnetic signal, an optical signal, and/or anyother suitable type of signal. These signals may be transmitted overcommunications links, such as wireless communications links, opticalfiber cable, coaxial cable, a wire, and/or any other suitable type ofcommunications link.

The different components illustrated for data processing system 900 arenot meant to provide architectural limitations to the manner in whichdifferent embodiments may be implemented. The different advantageousembodiments may be implemented in a data processing system includingcomponents in addition to and/or in place of those illustrated for dataprocessing system 900. Other components shown in FIG. 9 can be variedfrom the illustrative examples shown. The different embodiments may beimplemented using any hardware device or system capable of runningprogram code 918.

Thus, illustrative embodiments provide a method for designing a photonicswitching system that utilizes an equalized driver to increaseperformance of a photonic switch diode located on the silicon photonicchip. The descriptions of the various embodiments of the presentinvention have been presented for purposes of illustration, but are notintended to be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiment. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed here.

The flowcharts and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof various embodiments of the present invention. In this regard, eachblock in the flowcharts or block diagrams may represent a module,segment, or portion of code which comprises one or more executableinstructions for implementing the specified logical function(s). It alsoshould be noted that, in some alternative implementations, the functionsnoted in the blocks may occur out of the order noted in the figures. Forexample, two blocks shown in succession may, in fact, be executedsubstantially concurrently, or the blocks may sometimes be executed inthe reverse order, depending upon the functionality involved. It willalso be noted that each block of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by special purposehardware-based systems that perform the specified functions or acts, orcombinations of special purpose hardware and computer instructions.

The circuit as described above is part of the design for an integratedcircuit chip. The chip design is created in a graphical computerprogramming language and stored in a computer readable storage medium(such as a disk, tape, physical hard drive, or virtual hard drive suchas in a storage access network). If the designer does not fabricatechips or the photolithographic masks used to fabricate chips, thedesigner transmits the resulting design by physical means (e.g., byproviding a copy of the computer readable storage medium storing thedesign) or electronically (e.g., through the Internet) to such entities,directly or indirectly. The stored design is then converted into theappropriate format (e.g., GDSII) for the fabrication ofphotolithographic masks, which typically include multiple copies of thechip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

What is claimed is:
 1. A method for designing a photonics switchingsystem, the method comprising: designing, by a data processing system, aphotonic switch diode to attain each performance metric in a pluralityof performance metrics associated with a photonic switching system basedon a weighted value corresponding to each of the plurality ofperformance metrics; selecting, by the data processing system, anelectronic switch driver circuit design from a plurality of electronicswitch driver circuit designs for the photonic switching system;determining, by the data processing system, whether each performancemetric in the plurality of performance metrics associated with thephotonic switching system meets or exceeds a threshold valuecorresponding to each of the plurality of performance metrics based onthe photonic switch diode designed by the data processing system and theelectronic switch driver circuit design selected by the data processingsystem; responsive to the data processing system determining that eachperformance metric in the plurality of performance metrics associatedwith the photonic switching system meets or exceeds the threshold valuecorresponding to each of the performance metrics, designing, by the dataprocessing system, the photonic switching system using the photonicswitch diode designed by the data processing system and the electronicswitch driver circuit design selected by the data processing system thatmet or exceeded each threshold value corresponding to each of theplurality of performance metrics associated with the photonic switchingsystem based on the weighted value of each performance metric; andresponsive to the data processing system determining that eachperformance metric in the plurality of performance metrics associatedwith the photonic switching system does not meet or exceed the thresholdvalue corresponding to each of the plurality of performance metrics,re-designing, by the data processing system, the photonic switch diodeby increasing the weighted value of each performance metric that did notmeet or exceed its respective threshold value and decreasing theweighted value corresponding to a speed of the photonic switchingsystem.
 2. The method of claim 1 further comprising: receiving, by thedata processing system, the weighted value for each performance metricin the plurality of performance metrics associated with the photonicswitching system.
 3. The method of claim 1 further comprising: storing,by the data processing system, the photonic switching system designed bythe data processing system in a storage device.
 4. The method of claim1, wherein the plurality of electronic switch driver circuit designs isa current mode logic design, an inverter logic design, and an inverterlogic design coupled with an inductively peaked inverter logic design.5. The method of claim 1, wherein the electronic switch driver circuitdesign selected by the data processing system is a complementary metaloxide-semiconductor driver based on current mode logic employingfeed-forward equalization to drive the photonic switch diode.
 6. Themethod of claim 1, wherein the electronic switch driver circuit designselected by the data processing system is a complementary metaloxide-semiconductor driver based on inverter logic employingfeed-forward equalization to drive the photonic switch diode.
 7. Themethod of claim 1, wherein the electronic switch driver circuit designselected by the data processing system is a complementary metaloxide-semiconductor driver based on inverter logic and inductivelypeaked inverter logic generating a pre-emphasized drive waveform todrive the photonic switch diode.
 8. The method of claim 7, wherein thecomplementary metal oxide-semiconductor driver based on the inverterlogic and the inductively peaked inverter logic uses inductive peakingto enable one of overshoot, undershoot, or both overshoot and undershooton the pre-emphasized drive waveform exiting the electronic switchdriver circuit.
 9. The method of claim 1, wherein the photonic switchingsystem includes two electronic switch driver circuits, each of the twoelectronic switch driver circuits is powered by a separate supplyvoltage, wherein the photonic switching system uses an edge detectorcircuit to switch between drive waveform outputs of the two electronicswitch driver circuits at different times.
 10. The method of claim 1,wherein the plurality of performance metrics associated with thephotonic switching system is a speed of the photonic switching system, asize of the photonic switching system, power consumption of theswitching system, alignment tolerance of the photonic switching system,and cost of the photonic switching system.
 11. The method of claim 1,wherein the weighted value is a value assigned to each of the pluralityof performance metrics that indicates a level of importance of each ofthe plurality of performance metrics in designing the photonic switchingsystem.
 12. The method of claim 1, wherein the data processing systemdetermines that each performance metric in the plurality of performancemetrics associated with the photonic switching system meets or exceedsthe threshold value corresponding to each of the performance metrics byusing a simulation program.
 13. The method of claim 1, wherein the dataprocessing system determines that each performance metric in theplurality of performance metrics associated with the photonic switchingsystem meets or exceeds the threshold value corresponding to each of theperformance metrics by analyzing test data.
 14. The method of claim 1,wherein the photonic switch diode is included in an active siliconphotonic layer of a silicon photonic chip.
 15. The method of claim 14,wherein the electronic switch driver circuit is located on the siliconphotonic chip.
 16. The method of claim 1, wherein the photonic switchdiode includes a plurality of input ports and a plurality of outputports to receive and transmit optical signals encoded with data.
 17. Themethod of claim 1, wherein the photonic switch diode is driven by apre-emphasized drive waveform that is generated by the electronic switchdriver circuit from an electronic control signal input received from anoptical packet scheduler.
 18. The method of claim 1, wherein theelectronic switch driver circuit waits a predetermined amount of guardtime to ensure that a state of the photonic switch diode has changedprior to the electronic switch driver circuit applying a drive waveformto the photonic switch diode.
 19. The method of claim 18, wherein thestate of the photonic switch diode is changed between transmission ofeach optical packet.